Coating process and coating promoter compounds for bullets



2,999,767 COATING PROCESS AND COATING PROMOTER COMPOUNDS FOR BULLETSFranklin B. Clay, Jr., Westport, Joseph F. Kenney,

Bridgeport, Marshall J. Kidder, Fairfield, and Raymond H. Vandenberg,Stratford, Conn., assignors to Remington Arms Company, Inc., Bridgeport,Comn, a corporation of Delaware No Drawing. Filed Jan. 16, 1959, Ser.No. 787,123

7 Claims. (Cl. 117-109) This invention relates to the discovery ofcertain chemicals which constitute improved coating promoter compoundsand which make possible an improved meth od for metal coating variousmetal articles without the use of electrical energy, heat or moltenmetal.

It is a general object of this invention to provide an improved processfor forming protective metallic coatings on metal articles, which methodis economical to carry out, simple in operation, and produces a verystrong coating of high quality on the articles.

Another object is the provision of a new and improved coating or platingpromoter chemicals Which enable the process to be carried out with theaddition of a minimum amount of chemical additives and makes possibleand feasible the continued reuse of such chemicals in subsequent batchesof the coating operation.

More particularly, the improved process and promoter compound of thisinvention has for its object the rapid and economical coating ofprojectiles for firearm cartridges with brass, to improve both theappearance, storage qualities, and the performance characteristics ofsuch projectiles.

A general process of somewhat similar nature is disclosed in BritishPatent No. 534,888, dated March 21, 1941, and subsequent improvementstherein have appeared with the issue of the following United Statespatents: No. 2,640,001, issued May 26, 1953, to E. T. Clayton; Re.23,861, issued Aug. 31, 1954, to E. T. Clayton; and No. 2,689,808,issued Sept. 21, 1954, to E. T. Clayton.

The method of applying the metallic coating to metallic articlesgenerally involves a container or drum mounted for suitable agitationsuch as revolving or tumbling, a group of articles to be plated, aquantity of metal to form the desired coating, in finely divided powderform, and a solution containing certain chemicals which assist andaccelerate the coating process. The articles to be coated, the powderedmetal, and impact media, such as shot, if desired, and the solutioncontaining the chemicals, are all placed in the drum which is thenagitated until the powder is converted into a uniform coating on thearticles by the effects of the tumbling. The physical and chemicalphenomena which are generally believed to take place are discussed inthe above referenced patents.

It is, of course, a much sought-after commercial objective to achieve adense uniform coating on the articles within a minimum time and With themost economic or minimum expenditure of promoter chemicals. The improvedcoating promoter compounds of applicants invention not only achieved avery excellent coating in a short time but by reason of their ability tobe reused, make possible an improved and far more economical process.Smaller quantities of the promoter chemicals are required for each batchof articles coated.

The improved process of applicants invention is related to the discoveryby them of compounds which can be used for promoting metal plating andwhich are superior to those heretofore knownv A simplified flow diagramof the process is as follows:

Metal articles such as lead bullet slugs Tumble in plating promoterone-halt hour Add powdered metal such as brass tumble one-half hour lgorreuse if desired Drain Wash and dry Filter metal articles solutionFortiiy with citric acid weight:

Percentage by Weight Octyl trimethyl ammonium chloride 1.67 Decyltrimethyl ammonium chloride 1.88 Dodecyl trimethyl ammonium chloride17.29 Tetra decyl trimethyl ammonium chloride 4.50 Hexadecyl trimethylammonium chloride 17.09 Octadecyl trimethyl ammonium chloride 2.46Octadecenyl trimethyl ammonium chloride 3.25

'Octadecadienyl trimethyl ammonium chloride 1.88 Isopropanol 35.30Sodium chloride 1.00 Water 13.70

The range of proportions of the ammonium salts are set forth as follows:

From min. of

'Octyl trimethyl ammonium chloride 0.2% up Decyl trimethyl ammoniumchloride 0.2% up Dodecyl trimethyl ammonium chloride 1.7% up Tetra decyltrimethyl ammonium chloride 0.5% up Hexadecyl trimethyl ammoniumchloride 1.7% up Octadecyl trimethyl ammonium chloride 0.3% upOctadecenyl trimethyl ammonium chloride 0.3% up Octadecadienyl trimethylammonium choride..- 0.2% up The isopropanol and sodium chloridepercentages remain constant. The practical upper limits of the ammoniumchloride salts are determined by the point at which at least all thevarieties, of the salt in the above minimum quantifies can be added.Excess amounts of any of these salts were not found to adversely afiectthe plating process below acceptable limits although these limits wereconsiderably below the optimum limits of the preferred proportions. Theformulation must include at least one and preferably at least threedifferent salts from the group of ammonium salts discussed above.

The specifications for a charge of material to be placed into theagitating or tumbling drum for one coating cycle are set forth asfollows:

20 lbs. of lead slugs,

10 ml. of the aforementioned isopropanol-ammonium chloride compound,

0.75 oz. of citric acid,

290 ml. of water,

2.5 oz. of brass powder (80% through 325 mesh, 100% through 100 mesh).

After charging all of this material except the brass powder into thedrum, the drum is tumbled for one-half hour. Next, the brass powder isadded and the drum is tumbled for a total of one hour. The drumcircumferential speed should be in the vicinity of 147 feet per minutefor a cylindrical drum with a roughened interior having a diameter ofseven inches. The solution is drained ofi, filtered, or settled toremove any sludge, and returned for reuse after addition of citric acid.The plated slugs or articles are washed and dried and then moved ontothe next processing step, if any.

It has been determined that the concentration of the isopropanol mixturedescribed above can be varied from 5 ml. per hundred pounds of leadarticles or slugs to as high as 300 ml. per hundred pounds. A preferredoptimum operating range for lead bullets lies in the area from 25 to 100ml. per hundred pounds of articles to be coated.

The use of applicants improved coating promoter agent makes possible animproved and economical process in which substantially smallerquantities of promoter chemicals are used and in which the promoteragent can be reused. In addition, the coating takes place in a shorttime period and results in a very dense adherent strong coating of ahighly attractive nature and capable of surviving the subsequent swagingoperation.

The process may conveniently be carried out at ordinary ambienttemperatures. No heat input is required.

Although, in accordance with the patent statutes, we have in the abovespecification disclosed a preferred embodiment of our invention, it isdesired that the scope of our invention be determined by the language ofthe appended claims.

We claim:

I. The method of metal coating successive groups of metal articlescomprising mixing a batch of said articles with an aqueous solution ofan organic film-forming coating promoter agent comprismg a weak organicacid and a plurality of salts taken from the group consisting of thealkyl and alkenyl trimethyl ammonium halides, agitating said mixture andspreading said coating agent as organic molecular films on the metalsurfaces, adding a quantity of metal powder particles and by tumbling ina rotating drum developing high pressures between the metal surfaces ofsaid articles and the particles of metal powder to part said films atthe areas of contact and bring said surfaces together in metal-to-metalcontact with each other and deposit and attach said particles to thearticle surf-aces and to each other to deplete said particles of metalpowder in the solution and build up said particles into continuous densestrongly adherent metal coatings on the surfaces of said articles to thedesired thickness, removing said group of articles, separating, cleaningand resupplying said aqueous solution and a new group of articles intomixture for continuation of the process.

2. A mixture for use as an additive coating promoter agent in a methodof applying a metallic coating to metallic articles by rotating in adrum 2. group of articles to be plated, a quantity of powdered metalparticles to form the coating and a liquid carrier, said mixturecomprising the following composition of materials by weight:

the liquid carrier comprising a citric acid-water solution and theweight proportions of metal articles to carrier to promoter agent beingabout 900:3021.

3. A mixture for use as the carrier liquid and plating promoter agent ina process for the metal plating of metallic articles by tumbling thearticles to be plated, a quantity of metal powder to form the plate, anda liquid together in a rotating drum comprising a water solution ofcitric acid, isopropanol and a plurality of salts taken from the groupconsisting of the alkyl and alkenyl trimethyl ammonium salts, each salttaken from such group containing from eight to eighteen carbon atoms.

4. A metal plating agent for assisting in coating lead bullets withbrass powder in a tumbling process comprising a water solution of a weakorganic acid and a plurality of salts taken from the group consisting ofthe alkyl and alkenyl trimethyl ammonium halides, the pluralitycontaining at least three dilierent salts each salt taken from suchgroup having from eight to eighteen carbon atoms.

5. A method of mechanically plating a group of lead bullets with brasscomprising mixing said bullets with an aqueous solution containing aweak organic acid, an alcohol and a plurality of salts taken from thegroup consisting of three to eight different alkyl and alkenyl trimethylammonium halides each having the alkyl and alkenyl group of each varyingfrom eight to eighteen carbon atoms, agitating said mixture, adding aquantity of brass powder, agitating said mixture and brass powder untilsaid powder has been transformed into a continuous dense, uniformadherent coating on the exterior surfaces of said bullets, separatingsaid bullets from said mixture and washing said bullets.

6. A mixture for use as an additive coating promoter agent in a methodof applying a metallic coating to metallic articles by rotating in adrum a group of articles to be plated, a quantity of powdered metalparticles to form the coating and a liquid carrier, said mixturecomprising the following composition of materials by weight:

Octyl trimethyl ammonium chloride; At least 0.2%. Decyl trimethylammonium chloride At least 0.2%.

the liquid carrier comprising a citric acid-water solution.

7. A metal plating agent for assisting in coating lead bullets withbrass powder in a tumbling process comprising a Water solution of a Weakorganic acid and a plurality of salts taken from the group consisting ofthe alkyl and alkenyl trimethyl ammonium halides, the pluralitycontaining at least one salt having from eight to eighteen carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS Sloanet a1 Nov. 12, 1940 Young May 27, 1947 Clayton May 26, 1953 WrotnowskiMar. 29, 1960

1. THE METHOD OF METAL COATING SUCCESSIVE GROUPS OF METAL ARTICLESCOMPRISING MIXING A BATCH OF SAID ARTICLES WITH AN AQUEOUS SOLUTION OFAN ORGANIC FILM-FORMING COATING PROMOTER AGENT COMPRISING A WEEK ORGANICACID AND A PLURALITY OF SALTS TAKEN FROM THE GROUP CONSISTING OF ALKYLAND ALKYENYL TRIMETHYL AMMONIUM HALIDES, AGITATING SAID MIXTURE ANDSPREADING SAID COATING AGENT AS ORGANIC MOLECULAR FILMS ON THE METALSURFACES, ADDING A QUANTITY OF METAL POWDER PARTICLES AND BY TUMBLING INA ROTATING DRUM DEVELOPING HIGH PRESSURE BETWEEN THE METAL SURFACES OFSAID ARTICLES AND THE PARTICLES OF METAL POWDER TO PART SAID FILMS ATTHE AREAS OF CONTACT AND BRING SAID SURFACES TOGETHER IN METAL-TO-METALCONTACT WITH EACH OTHER AND DEPOSIT AND ATTACH SAID PARTICLES TO THEARTICLE SURFACES AND TO EACH OTHER TO DEPLETE SAID PARTICLES OF METALPOWDER IN THE SOLUTION AND BUILD UP SAID PARTICLES INTO CONTINUOUS DENSESTRONGLY ADHERENT METAL COATINGS ON THE SURFACES OF SAID ARTICLES TO THEDESIRED THICKNESS, REMOVING SAID GROUP OF ARTICLES, SEPRATING, CLEANINGAND RESUPPLYING SAID AQUEOUS SOLUTION AND A NEW GROUP OF ARTICLES INTOMIXTURE FOR CONTINUATION OF THE PROCESS.